Research On The Arc Morphology And Weld Formation Of X100 High Strength Pipeline Steel Welede By Ultrasonic Pulse TIG Welding

Pulse TIG welding has attracted widely attention because its good welding quality and high efficiency.In accordance with the high-strength pipeline welding requirement of construction of oil and gas long-distance pipeline projects,the welding system based on the ultrasonic DC pulse TIG welding power source has been proposed to flat plate overlay welding tests on X100 pipeline steel,aiming to improve the welding quality of X100 pipeline steel welded joints by adjusting the welding performance of the arc heat source through the study of the physical and process characteristics of the arc.The fully automated welding system containing information detection and recording of the welding process has been established.The system is based on a self-developed dual DSP parallel-controlled ultrasonic DC pulse TIG welding machine,which can achieve high-power welding process and the real-time acquisition of morphology and electrical parameters of highfrequency pulse arc.Tests were carried out based on this welding system.The arc pattern and its electrical parameters were observed in real time in different pulse frequencies and duty cycles.The results show,the arc morphology is more sensitive to changes in pulse frequency relative to duty cycle.with the pulse frequency and duty cycle increasing,the arc morphology from a fan shape in low frequencies to a bell,showing radial compression and axial stretch.The effect of the arc energy pulse current parameters on the arc energy is analyzed in conjunction with the arc morphology and electrical parameter with multi-cycle acquisition.The peak arc voltage presents a ascend tendency with the increase of pulse frequency.The base arc voltage remains low and fluctuates in a small range,and the effective voltage increases slowly.Single factor cycle tests were carried out.The influence of the process parameters on the weld formation was studied and it was found that an increase in the base current had a small effect on the weld formation coefficient.With the increase in peak current and duty cycle,the depth and width of the weld increased.When the pulse frequency increases from20 k Hz to 50 k Hz,the penetration width decreases by 8.8% and the penetration depth increases by 10.3%.And with the increase in welding speed,the penetration depth and width decreased.A four-factor,three-level orthogonal test was carried out based on a single-factor cyclic test.Response surface analysis was used to investigate the effect of each fitting factor and its interaction on the response value weld forming factor.The optimum process parameters were determined to be a base current of 100 A,a peak current of 150 A,a pulse frequency of 50 k Hz and a duty cycle of 40%.And The perturbations of the process parameters on the weld forming factor were ranked as follows: pulse frequency > peak current >duty cycle > base current.A "V" bevel filler welding process test was carried out to verify that a well-formed and defect free welded joint was obtained.The microstructure of the weld was observed and it was found that the optimized process parameters were used for welding,the columnar crystal transformed to equiaxed crystal,the weld tissue grains became fine and the width of the fusion zone became narrower.Based on the tissue alteration properties,the weld area has a hardness of 340HV10,a tensile strength of820 MPa and a maximum impact work of 214 J.The results of the mechanical tests show that the weld area of the joint welded by ultrasonically induced welding has better resistance to plastic deformation than the parent material.The weakest area of the weld was reduced,the weldability of the X100 pipe line steel was improved and the toughness of the X100 high tensile pipe line steel weldment was increased.